docs: def extract_assets(dstore, what):
      """
      Extract an array of assets, optionally filtered by tag.
      Use it as /extract/assets?taxonomy=RC&taxonomy=MSBC&occupancy=RES
      """
      qdict = parse(what)
      dic = {}
      dic1, dic2 = dstore['assetcol/tagcol'].__toh5__()
      dic.update(dic1)
      dic.update(dic2)
      arr = dstore['assetcol/array'].value
      for tag, vals in qdict.items():
          cond = numpy.zeros(len(arr), bool)
          for val in vals:
              tagidx, = numpy.where(dic[tag] == val)
              cond |= arr[tag] == tagidx
          arr = arr[cond]
      return ArrayWrapper(arr, dic)